1969 427/435 L89 Valve Adjustment

[Kevin C.]

I'm trying to adjust the valves on my 427/435 engine with solid lifters and I know the stock spec's are .024 Intake/.028 Exhaust. My question is are these spec's for a "hot" engine or "cold" engine? The heads are the original 3919842 closed chamber aluminum heads ---should there be any adjustment to the clearances because they are aluminum? I've owned the car almost 25 years and I haven't set the valves in a long time and I can't remember what clearances I used. Thanks!

Kevin C.

[Duke W.]

Re: 1969 427/435 L89 Valve Adjustment

On a cast iron engine there is very little difference between hot and cold clearance because the cast iron head and block expand about as much as the steel pushrod and valve stem.

Based on my experience with DOHC four valve aluminum engines, the valve clearance opens up about two thou when hot because the aluminum head and cam carrier expand more than the valve stem.

Based on this I would recommend that you set them two thousanths tighter than the recommended clearance for the L71. If the BB is like the SB you need to snug them down about another two thou to compensate for actual rocker geometry. I expect the big block shows similar deviation from specified rocker geometry, but I have never measured the BB rocker geometry. The SB rocker ratio starts at about 1.37:1 at the top of the clearance ramp and maxes out at about 1.44 with OEM maximum valve lift. That's a lot different than the specified (and constant) 1.5:1 that everyone takes as gospel!

You can use the 30-30 cam cold engine not running adjustment procedure to ensure you are on the base circle for each valve. If you would like it, e-mail me and I'll send you the Word file.

Duke

[Clem Z.]

Re: 1969 427/435 L89 Valve Adjustment

allow .004 tighter when cold on a BBC with iron block and aluminum heads. allow .010 if you have aluminum block and heads

[Duke W.]

Re: 1969 427/435 L89 Valve Adjustment

Sounds good to me, Clem. I was going to recommend that Kevin go with .020"/.024" cold, but I wanted to hear what you had to say. Kevin e-mailed me and said he has an old P&G valve clearance tool that he picked up at a swap meet, but he wasn't sure how to use it. I figure you know that one, too.

Duke

[Clem Z.]

Re: 1969 427/435 L89 Valve Adjustment

hi duke, mrs clem and i are in daytona for the races. the P&G needs a special adapter for each size valve spring retainer and unless he has all the adapters it may not work and they are to be used when the engine is running and that means a big mess to clean up when you are done. go to www.google.com and punch in P&G valve gapper and see what comes up.